Update root-composer to v6

Author: renovate-bot

composer.json

@@ -26,14 +26,14 @@
     "phpstan/phpstan-phpunit": "^1.0",
     "phpstan/phpstan-strict-rules": "^1.0",
     "phpunit/phpunit": "^9.5",
-    "symfony/config": "^4.2 || ^5.0",
-    "symfony/console": "^4.0 || ^5.0",
-    "symfony/form": "^4.0 || ^5.0",
-    "symfony/framework-bundle": "^4.4 || ^5.0",
-    "symfony/http-foundation": "^5.1",
-    "symfony/messenger": "^4.2 || ^5.0",
+    "symfony/config": "^6.0",
+    "symfony/console": "^6.0",
+    "symfony/form": "^6.0",
+    "symfony/framework-bundle": "^6.0",
+    "symfony/http-foundation": "^6.0",
+    "symfony/messenger": "^6.0",
     "symfony/polyfill-php80": "^1.24",
-    "symfony/serializer": "^4.0 || ^5.0"
+    "symfony/serializer": "^6.0"
   },
   "config": {
     "platform": {